This invention is directed to commercial or residential heat pump systems that provide heating or cooling of a comfort zone as required. More particularly, this invention is directed to a method and apparatus for controlling and preventing freeze-up of the indoor coil in a heat pump and air conditioner.
Heat pumps are often employed to provide heating or cooling, as needed, to a residential or commercial comfort zone, i.e., the interior of a residence, office, hospital or the like. Systems of this type can have a number of modes of operation such as air conditioning alone, space heating alone, and various combinations thereof. Under certain conditions, water vapor in the air can freeze on the indoor coil when the device is operated in the air conditioning mode and the coil temperature drops below normal operating temperatures. Formation of ice on the indoor coil leads to loss of cooling capacity and eventual shut down of the system due to low refrigerant pressure. The causes of this freezing up may include low air flow, low outdoor temperatures, loss of refrigerant, and low refrigerant flow.